1. Field of the Invention
This invention relates to an image forming apparatus for effecting the formation of images such as characters and figures on a recording medium such as a recording sheet being conveyed, and more particularly to an image forming apparatus in which, for example, a plurality of mechanisms such as a recording medium conveying mechanism and a recovering mechanism for an ink jet head for effecting image formation are driven by a single drive source.
2. Related Background Art
In recent years, with the spread of personal computers, word processors, facsimile apparatuses, etc. in offices, etc., various image forming apparatuses have been provided as the information output apparatuses of these apparatuses. Above all, image forming apparatuses such as ink jet printers for discharging ink to a recording medium to thereby form images such as characters and figures thereon are excellent in the dignity of image, printing speed, apparatus size, the balance of prices, etc. and are also easy to color and therefore are widely spread, and are used as image forming apparatuses in various fields.
Now, an image forming apparatus of this type such as an ink jet printer is generally provided with a recovering mechanism for removing thickened ink, dust, etc. adhering to the discharge ports of an ink jet head to thereby maintain a stable ink discharging function.
As such recovering mechanisms, there are known a capping mechanism having a cap for covering a surface in which the discharge ports of the ink jet head are disposed during non-recording to prevent the drying or evaporation of the ink, a wiping mechanism for removing the ink adhering to the surface in which the discharge ports of the ink jet head are disposed by the use of a blade or the like, a suction mechanism for sucking thickened ink, etc. from the discharge ports of the ink jet head or the vicinity thereof through the above-mentioned cap, etc. This suction mechanism brings the interior of the cap covering the surface in which the discharge ports are disposed into negative pressure by a pump to thereby discharge the ink from the discharge ports or the like.
Also, in the image forming apparatus, a mechanism for feeding and conveying recording mediums generally comprises an automatic sheet feeding mechanism containing a plurality of recording mediums such as recording sheets therein and separating and feeding them one by one therefrom, and a conveying mechanism disposed downstream thereof for conveying the recording medium in synchronism with image formation. The automatic sheet feeding mechanism is provided with a sheet feeding roller for pressure-contacting with the uppermost one of the stacked recording mediums and picking up and feeding the uppermost recording medium by the rotation thereof. A frictional member for usually producing an appropriate frictional force sheet feeding is provided in the pressure contact portion of this sheet feeding roller. Also, the conveying mechanism is provided with a conveying roller rotated by obtaining a driving force from a drive source, a driven roller cooperating with the conveying roller to nip the recording medium therebetween, and a paper path for the recording medium to pass between these rollers. In the sheet feeding and conveying mechanisms as described above, the recording medium fed by the sheet feeding roller is usually subjected to the adjustment (referred to also as the registration) of the conveyed position thereof in a nip portion comprised of the conveying roller and the driven roller, whereafter it is conveyed in synchronism, for example, with the scanning of the ink jet head, by the conveying roller and the driven roller, and image formation is effected.
The sheet feeding roller is generally formed with a dead zone portion which does not contact with the recording medium in conformity with rotation to decrease the conveying load thereof. This dead zone portion is designed to return to a rotated position opposed to a recording medium fed next when the sheet feeding roller effects rotation for sheet feeding and has finally effected one full rotation. Also, control is effected so that when the one full rotation of this sheet feeding roller is completed, the conveying roller on the downstream side may start the conveyance of the fed recording medium.
In the sheet feeding and conveying mechanisms as described above, motors are often used as drive sources for driving the sheet feeding roller and the conveying roller. In this case, there are a construction in which the sheet feeding roller and the conveying roller are driven by a motor, and a construction in which the driving of the sheet feeding roller and the conveying roller is controlled by discrete motors.
There is also known a construction in which a drive source for the pump in the above-described recovering mechanism is common to that for the conveying roller or the sheet feeding roller and the respective operations thereof are controlled, for example, by the changeover of the forward and reverse rotations of the motor. Specifically, the ordinary conveyance of the recording medium is effected by the forward rotation driving of the motor for driving the conveying roller, and the pump is operated by the driving of the motor in the reverse direction. In this case, the driving force is transmitted from the motor to the pump through a so-called one-way drive transmitting mechanism, whereby even when the driving of the motor is done in a direction in which the conveying roller is forwardly rotated, the driving force is prevented from being transmitted to the pump.
In the above-described construction, when the sheet feeding roller effects one full rotation for sheet feeding and performs the operation of the dead zone thereof returning to the initial position opposed to the uppermost recording medium (hereinafter referred to also as the resetting operation), the recording medium may sometimes be conveyed slightly excessively. At this time, the conveying roller on the downstream side is also being driven and as the result, the recording start position of the recording medium may sometimes deviate delicately.
Therefore, in the above-described construction wherein a common drive source is used for the conveying roller and the pump, i.e., the construction wherein the ordinary conveyance of the recording medium by the conveying roller is effected by only the driving of the drive source in the forward direction, and the driving thereof in the reverse direction is used for only the driving of the pump, it has heretofore been proposed regarding the fine adjustment of this recording start position to utilize a pendulum gear transmitting mechanism which is a one-way drive transmitting mechanism, and effect the minute reverse rotating operation of the conveying roller within the movement range of the pendulum of this pendulum gear transmitting mechanism (the dead zone range of transmission in which transmission is not effected), thereby effecting the adjustment of the recording start position.
However, in the case of a recording medium which is liable to slip during the feeding thereof by the sheet feeding roller depending on the relation between the conveyance distance of the recording medium by one full rotation of the sheet feeding roller and the distance of the paper path, or when the environment is a predetermined image forming environment regarding temperature, humidity, etc., it is sometimes the case that by the one full rotation of the sheet feeding roller, the recording medium does not arrive at the nip portion and the sheet feeding roller must be rotated by more than one full rotation. Even when the sheet feeding roller need thus be further rotated it has been necessary to further continue the rotation thereof in order to perform the above-described resetting operation of the dead zone portion of the sheet feeding roller.
Therefore, in the above-described adjustment of the recording start position, the reverse rotation of the conveying roller is effected more than in the case of ordinary fine adjustment, whereby the movement range of the pendulum of the pendulum gear transmitting mechanism exceeds the range of the dead zone of the transmission thereof and the pendulum may reach a position in which it comes into engagement with the driving mechanism for the suction pump. As the result, in some cases, the initial position regarding the pump driving has deviated from a predetermined position and has caused the malfunctioning of the pump driving.
FIGS. 9 to 13 of the accompanying drawings specifically illustrate this problem.
In these figures, the reference numeral 1 designates sheets which are recording mediums and are stacked and contained in a sheet feeding tray 101 (only the uppermost sheet is designated by 1a). The reference numeral 102 denotes a sheet feeding roller comprising an arcuate portion provided with a frictional member for contacting with the sheet 1 and imparting a sheet feeding force during sheet feeding, and a chord-shaped portion constituting a dead zone portion which does not contact with the sheet 1 in the initial position thereof, and having a D-shaped cross-section as a whole. In the shown example, this sheet feeding roller is designed to be capable of being driven independently of a conveying roller. Also, the initial position of the sheet feeding roller 102 can be confirmed by a sensor, not shown, for detecting the rotated position of the sheet feeding roller. This initial position refers to a position in which the dead zone portion of the sheet feeding roller 102 is opposed to the sheet 1 and the sheet feeding roller 102 does not contact with the sheet 1, and the operation of rotating the sheet feeding roller to this initial position is the above-described resetting operation (the position shown in FIGS. 12 and 13).
When the sheet feeding roller 102 begins to be rotated from this reset position in the direction of arrow A indicated in FIG. 9, etc., the sheets 1 upwardly biased by a spring or the like, not shown, are brought into pressure contact with the arcuate portion of the sheet feeding roller 102, whereby the uppermost sheet 1a is fed in the direction of arrow B indicated in FIG. 9, etc. by a frictional force acting between it and the arcuate portion. This fed sheet 1a is then guided by a paper pan 309 and directed to the conveying roller 302. At this time, the rotation of the conveying roller 302 is stopped, and the fed uppermost sheet 1a is rammed against a nip portion formed by the conveying roller 302 and a driven roller 307 and a loop of a moderate size is formed, whereby the registration of the sheet is effected.
However, due to the various causes set forth above, as shown in FIG. 9, the sheet 1a may sometimes not arrive at the nip portion by the one full rotation of the sheet feeding roller 102. In such case, sheet detecting means (not shown) for detecting the arrival of the sheet at a predetermined position on a sheet path detects that the sheet has not yet arrived at the nip portion. In response to this detection, the second one full rotation of the sheet feeding roller 102 is started.
Thereby, as shown in FIG. 10, the leading end of the uppermost sheet 1a arrives at the nip portion, and a loop of a moderate size is formed and registration becomes effected. Usually, the distance deficient for the sheet to arrive at the nip portion by the first one full rotation is relatively smaller than the amount by which the sheet is fed by the first one full rotation of the sheet feeding roller and therefore, it is often the case that the state in which the sheet has arrived at the nip portion is immediately after the second one full rotation of the sheet feeding roller 102 has begun. Thus, the amount by which the sheet 1a is fed from this state by the sheet feeding roller 102 is relatively great.
That is, as shown in FIG. 11, in response to the arrival of the sheet at the nip portion, the conveying roller 302 begins to be rotated in the direction of arrow C indicated in FIG. 11, whereby the sheet 1a which has so far bumped against the nip portion is conveyed to a recording position on a platen 301 opposed to a recording head 201, and at this time, the sheet feeding roller 102 also effects a relatively great amount of rotation in the direction of arrow A as described above. As the result, as shown in FIG. 11, the sheet 1a passes the recording start position by the recording head 201 and is conveyed farther.
In contrast, in the conveying mechanism, as described above, the reverse rotation of the conveying roller is effected and the control of returning the sheet to the recording position is effected. That is, as shown in FIG. 12, after the resetting operation of the sheet feeding roller 102 is completed, the conveying roller 302 is rotated in a reverse direction (the direction of arrow D indicated in FIG. 12) to thereby move the uppermost sheet 1a in the direction of arrow E in order to return the too much fed uppermost sheet 1a to the recording position (a cue position).
At this time, in the construction as shown in FIG. 12 wherein a motor which is the drive source of the conveying roller 302 is used also as the drive source of a suction recovery pump, an LF pendulum arm 310 which is a one-way drive transmitting mechanism for the changeover of the driving thereof begins to rotate in the direction of arrow F.
However, as described with reference to FIG. 11, during sheet feeding, the sheet is fed relatively much past the cue position and the amount of return of the sheet by the reverse rotation of the sheet feeding roller 102 is great and therefore, the above-mentioned rotation of the LF pendulum arm does not fall within the transmission dead zone range, and when as shown in FIG. 13, the uppermost sheet 1a is returned to the cue position, an LF planetary gear 311 is rotated to a position in which it is engaged with a pump transmission gear 509. As the result, a driving force is transmitted to the pump transmission gear 509 and a pump cam 510 is rotated, whereby a detected member 510a provided on the pump cam 510 may sometimes arrive at the position of an initial position detecting sensor 550. In such case, the malfunctioning that the pump cam detects the arrival at the initial position and the sequence thereafter is started may be caused. For example, even if an attempt is made to effect the detection of the sensor for the initialization of another cam in a state in which the pump cam is detecting the detecting sensor, it may become impossible and malfunctioning may sometimes occur.
In order to solve such a problem, it is heretofore known to use discrete drive sources for the conveyance of the sheets and for the pump of the recovery system, and to discretely provide a complicated changeover mechanism with a carriage carrying a recording head thereon as the trigger for the changeover of the drive transmission to the pump. However, this has left problems in respect of the downsizing, simplification, lower cost, etc. of the apparatus.
It is an object of the present invention to provide an image forming apparatus in which a first mechanism is driven by the rotation of a drive source in a forward direction and a second mechanism is driven by the rotation of the drive source in a reverse direction and even when the first mechanism is driven by the rotation of the drive source in the reverse direction, the malfunctioning of the second mechanism is prevented.
It is another object of the present invention to provide an image forming apparatus having a drive source rotatable in forward and reverse directions, and drive changeover means for transmitting the driving force of the drive source, wherein the drive changeover means drives a first mechanism by the rotation of the drive source in the forward direction, and drives a second mechanism by the rotation of the drive source in the reverse direction, and even when the first mechanism is driven by the rotation of the drive source in the reverse direction, the malfunctioning of the second mechanism is prevented.